1. Field of the Invention
The present invention relates to a recording paper and an image recording method thereof. In particular, the invention relates to a recording paper using so-called plain paper having no coated layer containing substantial quantity of pigment on either surface thereof, and a image recording method for ink-jet printing and electrophotographic printing using the same.
2. Description of the Related Art
An image forming machine using an ink-jet printing method has characteristics such as: ease of coloring; low energy consumption; low noise generation during recording; and the ability to suppress production costs to low levels. Due to such advantages, image forming machines using ink-let printing methods have become widely used in offices in recent years, with increases in the number of machines which use ink-jet printing methods combined with electrophotographic image recording machines such as laser printers and copy machines.
Recording media (recording paper) such as so-called plain paper, coated paper and glossy paper for ink-jet printing, white film, and transparent film are used in image forming with ink-jet printing methods. Particularly when an image forming machine using ink-jet printing method is employed in an image forming machine of an electrophotographic printing method, such as a laser printer or copier in an office or the like, printing is conducted most often on plain paper. Among these machines most use plain paper, on which an image can be formed easily, which is readily available and at a low cost.
Therefore, enhancing the suitability for recording of plain paper image forming with ink-jet printing method is extremely important. However, there have been the following problems when printing is conducted on plain paper in conventional image forming with ink-jet printing methods.
(1) A so-called feathering phenomenon occurs whereby ink flows out along fibers in plain paper. Feathering significantly deteriorates image quality, particularly the quality of printed characters/letters.
(2) So-called plain paper usually contains a sizing agent on the surface for making the surface water-repellent. Consequently, absorption of ink is delayed, causing so-called inter-color bleeding (ICB) at portions where different colors contact with each other.
(3) Since absorption of the ink is delayed due to the water repelling properties of plain paper surfaces, faces which contact with printed surface become dirty when printed documents are stacked.
(4) Since colorants in the ink hardly stay on the surface of plain paper, the coloring nature of color ink is inadequate.
(5) Since the colorants in inks permeate into plain paper, printed images can be seen through from the back of plain paper—rendering double-sided printing impossible.
Ink-jet printers have attempted to produce high printing speeds comparable to that of laser printers, in accordance an expanded market for ink-jet printers in the office. However it has been very difficult to attain permeability (dryability) and image quality whilst also the ability to carry out double-sided printing.
To address these problems, Japanese Patent Applications Laid-Open (JP-A) Nos. 10-166713, 7-257017, 8-216498, 10-100531, 9-176995 and 2002-96547 have proposed methods for improving image quality by enhancing aggregation/precipitation of ink components using printing papers subjected to a surface treatment with cationic substances such as cationic polymers and polyvalent metal salts.
Of these methods, a method of adding a substance in advance to inks that increases the viscosity of the ink by reacting with a cationic substance applied to a surface of the printing paper is particularly useful for improving image quality. This is because non-uniform spread out rates of colorants contained in ink, when ink is applied to paper having the cationic substance on the surface can be controlled when high viscosity is obtained.
However, improved permeability (dryability) of the printing paper to the ink is the problem of the highest priority for ink-jet printers if a high printing speed comparable to that of the laser printer is desired. Accordingly, the recording printing paper used for the ink-jet printer compatible of such high speed printing is required to have the following characteristic. It is required to both accelerate permeation of the ink into the printing paper and also make ink components aggregate/precipitate within the very short period of time, after the ink has been printed on the surface of paper before the ink completes permeation into the printing paper.
Improvement of ink permeability (dryability) has been investigated by focussing on the processes of insolubilization/aggregation/precipitation of ink applied on a surface of printing paper. For example, regulation by using the quantity of ions eluted by cold water extraction for the printing paper has been proposed (JP-A Nos. 10-100532 and 61-74880).
For improving permeability (dryability) of the printing paper to ink focuss has been made on the processes of insolubilization/aggregation/precipitation of ink components printed on the surface of the printing paper. However, it has been difficult to comply with the required high speed permeability (dryability) of the ink, necessary for high speed printing, by using printing paper provided to conventional evaluation criteria for insolubilization/aggregation processes such as cold water extraction.
A printing paper used for ink-jet printing is required to have high ink permeability (dryability) that is compatible with high speed printing. In addition, generally it is becoming increasingly common that offices are equipped with both ink-jet printers and electrophotographic copy machines, used in the same office. Accordingly, a printing paper is required which is applicable to imaging by ink-jet printing as well as being sufficiently suitable to imaging using of electrophotographic methods.